The invention relates to a proportional activation magnet, in particular for a hydraulic valve.
The known activation magnets have a pole with a valve cone receiving bore for receiving a valve cone, and an essentially cylindrical pole tube with a pole tube bore for receiving an essentially cylindrical armature. In the known activation magnets, an air gap of approximately 0.1 mm to 0.4 mm is provided between the armature and the pole tube bore, or the armature space is open toward the external environment on the side of the armature tappet so that the hydraulic fluid can flow in and out into the armature space in an unthrottled fashion. Air and dirt can pass unimpeded into the armature space and disrupt the functioning of the proportional activation magnet. It is very difficult to remove the air completely from the long narrow gap between the armature and pole tube bore when venting the armature space provided in the pole tube. Furthermore, the known proportional activation magnets frequently have intermediate spaces and connecting bores in which air pockets form when they are filled with hydraulic oil.
Venting screws have not proven suitable here for venting because it would be necessary to provide a multiplicity of venting screws in order always to ensure venting from the highest point in the interior of the magnet when the installation position of the hydraulic solenoid valve changes.
Here, air bubbles which are present in the interior of the proportional activation magnet are particularly disadvantageous because they reduce the modular subcompression of the hydraulic fluid and thus considerably reduce the damping of the movement of the armature. This results in a situation in which the solenoid valve can easily be excited to oscillate, causing disruption in the operation of the hydraulic solenoid valve. In addition, dirt in the armature space can become caught in the armature bearing and thus lead to failure of the activation magnet.
The invention is therefore based on the object of making available a hydraulic solenoid valve and a proportional activation magnet, in particular for a hydraulic solenoid valve, with which reliable operation is always possible.
This object is achieved according to the invention by means of the subject matter of the independent claims. Advantageous developments emerge from the respective subclaims.
According to the invention, an armature tappet which has a smaller diameter than the armature and the valve cone is provided between the armature and valve cone. Furthermore, a retention area with a tappet passage opening is provided in the region between the valve cone receiving bore and pole tube around the armature tappet, an annular gap with a predetermined gap width being formed around the circumference of the tappet passage opening between the inside of the tappet passage opening and the outside of the armature tappet which extends in the tappet passage opening.
The invention accordingly provides for the hydraulic fluid to be capable of flowing in and out in a throttled fashion between the armature space and external surroundings on the side of the armature tappet so that a back pressure, which damps the movement of the armature, builds up in the armature space on the side of the armature tappet.
As a result of the region between the valve cone receiving bore and pole tube being formed according to the invention, good damping of the movement of the armature is always ensured. The hydraulic fluid which flows into the pole tube, or out of it, as a result of a movement of the armature in the pole tube must pass through the annular gap, in which case it is subject to a friction effect. As a result, the flow is subject to resistance which has a damping effect on the movement of the armature.
It is advantageous that the ingress of dirt and air into the pole tube is also effectively prevented by the embodiment with the annular gap around the armature tappet.
In the invention it has become apparent that a particularly advantageous solenoid valve with a proportional activation magnet is obtained if the diameter of the armature tappet is selected to be particularly small. On the one hand, this results in a low degree of exchange of oil between the pole tube and the valve cone receiving bore when the armature moves. On the other hand, given the same gap width the annular gap face is reduced in proportion with the diameter of the armature tappet. A small annular gap face increases the damping effect on the armature and reduces the risk of the ingress of air and/or dirt into the pole tube. In addition, the ingress of air and/or dirt into the pole tube is also counteracted by the low degree of exchange of oil between the pole tube and valve cone receiving bore. The armature tappet in the retention area should advantageously not experience friction in order to prevent any hysteresis of the activation magnet being increased.
With the embodiment according to the invention it has proven particularly effective to form the annular gap between the armature tappet and the tappet passage opening in such a way that the ratio of the gap width to the diameter of the armature tappet is smaller than 0.25 and in particular smaller than 0.05. This results in a good function if the annular gap width is 0.1 mm and if the tappet diameter is 2 mm. Given an armature diameter of 16.7 mm, reliable operation of the activation magnet according to the invention is then obtained. Further improvements are obtained if the annular gap is reduced still further, for example to dimensions of less than 0.1 mm. It is particularly advantageous here to embody the bearing of the armature in such a way that only a low degree of axial play occurs. Given such bearing of the armature, the gap width can in fact be reduced still further without the armature tappet experiencing friction in the retention area owing to the axial displacements of the armature, which would result in increased hysteresis of the activation magnet.
According to the invention, the gap width is to be embodied in such a way that when the armature moves there is marked damping of the movement of the armature owing to the throttling of the hydraulic oil in the annular gap.
With the embodiment of the activation magnet according to the invention the interior of the pole tube is also automatically vented so that venting screws can be dispensed with.
It is advantageous that the retention area is embodied as an essentially disk-shaped baffle plate which has the throttle passage opening arranged in its center. This results in particularly simple manufacture and mounting of the actuation magnet according to the invention.
Furthermore provided in the region between the outer surface of the armature and the pole tube bore is a film bearing which can also essentially completely fill the space between the outer surface of the armature and the pole tube bore. This results in a shape of the interior space of the pole tube which is such that air pockets can build up only with difficulty because the long narrow gap between the pole tube and armature is avoided by the film bearing.
In a further embodiment of the actuation magnet according to the invention, the pole tube can have, on its side facing away from the valve cone receiving bore, a closure lid which can contain various assemblies. It is therefore conceivable to embody the closure lid with an adjustment device for setting the working point of the armature. This can be done for example by providing an adjustment screw in the closure lid.
Furthermore, the closure lid can also have a restoring device for applying a restoring force to the armature. A restoring device which can in particular also project into the armature has proven effective for this. In this embodiment, the space which is taken up by the restoring device always has hydraulic fluid flowing through it which, during movements of the armature, moves within equalization bores provided in the armature. This effectively counteracts the formation and collection of air bubbles on the pole tube.
The restoring device exerts a restoring force on the armature and can be embodied in this respect in such a way that when the cone tip moves toward the valve seat a portion of the magnetic force is stored in two compression springs connected one behind the other in the armature movement direction. Here, an armature retraction spring is firstly slightly biased and the biasing force is limited by a stop. An oscillation damping spring is then further biased until the tip of the cone comes to rest in the valve seat. The spring constant of the oscillation damping spring is high. This spring is biased only by a few tens of millimeters. With this device, it is possible to carry out the zero point equalization of the set point pressure characteristic curve, pressure oscillations are damped and, given a set point value 0 after the oscillation damping spring is relieved of tension, the armature retraction spring retracts the armature against the closure lid stop face so that a small pressure gradient is brought out at the throttle gap between the valve seat and tip of the cone.
Finally, the armature can have a spring space which extends in the axial direction of the armature, from whose bore base at least one equalization bore extends to an end face of the armature. As a result, thorough scavenging of the armature with hydraulic fluid is ensured, counteracting the formation of air bubbles.